Method and plant for converting plastic into oil

ABSTRACT

A method and plant for conversion into oil is provided which can completely heat and decompose a large amount of a plastic raw material, and treat a harmful gas. The plastic raw material is dissolved in a dissolution section ( 31 ) to form an expanded plastic. The expanded plastic is sent to an inclined first-stage decomposition column ( 47 ) and a second-stage decomposition column ( 48 ) adjacent to the first-stage decomposition column, both having fixed temperature distributions, which depolymerize and decompose the plastic into a light secondarily decomposed gas. The extracted secondarily decomposed gas is cooled into oil in condensers ( 37, 38 ) and collected in oil storage tanks ( 42, 43 ).

TECHNICAL FIELD

The present invention relates to a method and a plant for convertingplastic into oil for collecting the oil from the plastic.

BACKGROUND ART

Various plants for collecting oil from plastic waste have been proposed,none of them, however, has sufficiently decomposed the plastic, andactually no plants are in practical operation.

The present applicants previously developed a plant for conversion intooil that has a compact and simple structure of an inverse thermalgradient type, which is disclosed in Japanese application patentlaid-open publication No. 2000-16774.

There have been problems, however, with this plant for conversion intooil, including: 1) the plant can reliably convert a small amount ofplastic into oil, but the plant cannot completely convert a large amountof plastic into oil, 2) the plant cannot sufficiently treat a hydrogenchloride gas that is generated in a dissolution section in dissolvingPVC (polyvinyl chloride) plastic, and 3) the plant cannot sufficientlytreat an off gas that has not been converted into oil.

The present invention has been mainly made in light of these problemsand a primary object of the present invention is to provide a method anda plant for conversion into oil, which are able to convert a largeamount of plastic into oil, to treat a hydrogen chloride gas, and tocompletely treat an off gas.

DISCLOSURE OF THE INVENTION

The method for conversion into oil according to the present inventioncomprises heating and dissolving the plastic into expanded plastic, andremoving the expanded plastic, heating and depolymerizing it, andcooling it into oil. The expanded plastic may preferably be removed bybeing lifted at an angle, preferably at an angle of 25-30° relative tothe horizontal. The expanded plastic may preferably be heated with beinglifted at an angle and the expanded plastic may preferably be heated tohigher temperatures at higher positions. The dissolved plastic maypreferably be added with vegetable oil or animal oil or mineral oil andheated to generate expanded plastic of their mixture.

The method for conversion into oil according to the present inventionmay preferably comprising separating a hydrogen chloride gas generatedin dissolving the plastic from other decomposed gases, then reacting thehydrogen chloride gas with hydrated lime, and collecting it as calciumchloride. An off gas not converted into oil may preferably be treated bycatalytically cracking the off gas with a hot ceramic.

A plant for conversion into oil according to the present inventioncomprises a dissolution section for heating and dissolving the plasticinto expanded plastic, and a decomposition section for removing theexpanded plastic, heating and depolymerizing it, and cooling it intooil. In this plant for conversion into oil, the decomposition sectionmay preferably comprise a removal means for removing the expandedplastic by lifting it at an angle, preferably at an angle of 25-30°relative to the horizontal. The decomposition section may preferablycomprise a heating means for heating the expanded plastic with liftingit at an angle and for heating the expanded plastic to highertemperatures at higher positions. The plant may preferably comprise anoil injection means for injecting vegetable oil or animal oil or mineraloil into a connection between the dissolution section and thedecomposition section. The dissolution section may preferably comprise aplurality of dissolution columns with different temperature ranges. Thedecomposition section may preferably comprise a plurality of tilteddecomposition columns with different temperature ranges.

The plant for conversion into oil according to the present invention maypreferably comprise a dechlorination system for treating a hydrogenchloride gas generated in the dissolution section. This dechlorinationsystem may preferably comprise a separator for separating the hydrogenchloride gas from other decomposed gases, and a reactor for reacting thehydrogen chloride gas separated by the separator with hydrated lime intocalcium chloride. The plant may preferably comprise an off gas treatmentsystem for treating an off gas not converted into oil after cooling inthe decomposition section by catalytically cracking the off gas with ahot ceramic.

The plant for conversion into oil according to the present invention maypreferably comprise a residual collection means at the top of the finalstage decomposition column of the multistage decomposition columns. Theresidual collection means may preferably comprise a column with itsupper opening at the top of the final stage decomposition column and itslower opening in an atmosphere of an inactive gas heavier than the air.

The plant for conversion into oil according to the present invention maypreferably comprise a hopper for storing and supplying the plastic intothe dissolution section, and the hopper may preferably comprise a leadscrew with a spiral blade. The plant may preferably comprise an unheatedsection formed as an unheated area of a predetermined length between thehopper and the dissolution section. The plurality of dissolution columnseach may preferably comprise a lead screw with a spiral blade forcarrying the plastic, and a beginning dissolution column of theplurality of dissolution columns may preferably comprise the lead screwblade with a greater pitch than the lead screws blades in otherdissolution columns.

In the plant for conversion into oil according to the present invention,the dissolution section and the decomposition section each maypreferably comprise: an inner column; an outer column around the innercolumn; a hot air space between the inner column and the outer columnand through which an hot air circulates; and a temperature sensor fordetecting a temperature in the dissolution section or the decompositionsection, and the plant may preferably further comprise a carbon dioxidegas supplying system for supplying the carbon dioxide gas into the hotair space if the temperature sensor detects an abnormal temperatureequal to or greater than a predetermined temperature.

In the plant for conversion into oil according to the present invention,the dissolution section and the decomposition section each maypreferably comprise: an inner column; an outer column around the innercolumn; and a hot air space between the inner column and the outercolumn and through which an hot air circulates, and the plant maypreferably further comprise: a hot air production system for generatingby combustion the hot air to be supplied into the hot air space; and adrying system for drying the plastic to be supplied into the dissolutionfurnace, and an air in the drying system may preferably be supplied intothe hot air production system to be deodorized by combustion. The air inthe drying system may preferably be supplied into the off gas treatmentsystem to be deodorized by being catalytically cracked with a hotceramic.

In the plant for conversion into oil according to the present invention,an extendable column which is extendably formed may preferably be usedin a part of the dissolution column includes, and the extendable columnmay preferably comprise: an inner column; a bellows around the innercolumn which has one end fixed on the inner column and an other endslidable relative to the inner column; and an outer column which isfixed on the other end of the bellows and slidably contains the innercolumn.

In the plant for conversion into oil according to the present invention,the dissolution section may preferably comprise: an inner column; anouter column around the inner column; and a heating medium space betweenthe inner column and the outer column and through which a liquid heatingmedium circulates, and the plant further may preferably comprise aheating medium supplying system for supplying the liquid heating mediuminto the heating medium space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of the basic principle of the presentinvention.

FIG. 2 shows a schematic diagram of an embodiment according to the basicprinciple of the present invention.

FIG. 3 shows a schematic perspective view of a plant of conversion intooil of an embodiment according to the present invention.

FIG. 4 shows a schematic front view of a plant of conversion into oil ofan embodiment according to the present invention.

FIG. 5 shows a schematic plan view of a plant of conversion into oil ofan embodiment according to the present invention.

FIG. 6 shows a schematic diagram of FIG. 5.

FIG. 7 shows a schematic diagram of FIG. 4.

FIG. 8 shows a schematic transverse cross sectional view of adissolution column.

FIG. 9 shows a schematic transverse cross sectional view of adecomposition column.

FIG. 10 shows a schematic diagram of a dechlorination treatment section.

FIG. 11 shows a schematic diagram of an off gas treatment section.

FIG. 12 shows a schematic diagram of another embodiment.

FIG. 13 shows a schematic diagram of a connection between a dissolutionsection and a decomposition section.

FIG. 14 shows recovery rates for different plastics to be treated.

FIG. 15 shows a schematic illustration of how to lift expanded plastic.

FIG. 16 shows a schematic transverse cross-sectional view of a hopper.

FIG. 17 shows a schematic perspective view of an unheated section.

FIG. 18 shows a schematic diagram of a sludge tank.

FIG. 19 shows a schematic diagram of an extendable column.

FIG. 20 shows a schematic diagram of an accident avoidance system and adeodorant system.

FIG. 21 shows a schematic diagram of another embodiment.

BEST MODES FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will be described belowreferring to the drawings.

FIG. 1 shows a conceptual diagram illustrative of the basic principle ofa method for converting plastic into oil according to the presentinvention. Plastic raw-material is dissolved at a temperature of200-350° C. and is stored in a storage section 1. A decomposition column13 lifts the plastic that is dissolved (dissolved plastic) at an angle.

The decomposition column 13 includes an inner column 2, an outer column6 which forms a hot air space 4 around the inner column 2, and a leadscrew 7. The lead screw 7 includes a rotating shaft 14 and a spiralblade 8. A motor 12 rotates the lead screw 7 at a speed of 4-5revolutions per minute. A pipe 10 supplies a hot air into the hot airspace 4 to hold the temperature of the inner column 2 at 350-620° C. forgasification and depolymerization of plastic.

The lead screw 7 carries through the inner column 2 the dissolvedplastic which is primarily decomposed (into the first heavy gas statethat is gasified from the dissolved state) in the lower part of thedecomposition column 13 to provide a primarily decomposed gas. The leadscrew 7 carries the primarily decomposed gas at a low speed to the upperpart of the decomposition column 13. The primarily decomposed gas isthen secondarily decomposed (into a state that is depolymerized from theplastic and can be cooled into oil) in the inner column 2 which is heldat 350-620° C. by the hot air supplied from a pipe 15, to provide alight secondarily decomposed gas.

One decomposition column is enough to sufficiently secondarily decomposeat the upper part of the decomposition column all oil componentsincluded in the plastic raw material. Two decomposition columns may beused of which the first stage decomposition column connects to thestorage section 1 and the second stage decomposition column connects tothe first stage decomposition column.

An outer case 5 resides outside the storage section 1 to form a hot airspace 3 into which a hot air is sent. The plastic supplied into thestorage section is heated to 200-350° C. to provide dissolved plastic mpwith foamed plastic (expanded plastic) f formed on its surface. Thisexpanded plastic f is heated with being lifted at an angle by a leadscrew 7 which has its tip 14 a immersed in the dissolved plastic mp.This can provide a larger contact area between the expanded plastic fand the heat to ensure the decomposition (depolymerization) of theexpanded plastic f into the secondarily decomposed gas. A pipe 9collects the secondarily decomposed gas, which is then cooled into oiland stored in an oil storage tank.

The expanded plastic f is preferably lifted at a speed of 30-60 cm/min.A lower speed will give less carrying efficiency and a higher speed willgive insufficient decomposition. For example, the lead screw 7 liftsspirally the expanded plastic f as shown in FIG. 15, preferably bymoving it spirally at a speed of 30-60 cm/min. This speed can beadjusted by, for example, the pitch p of the lead screw 7. The expandedplastic f is thus carried at the above-described speed and heated slowlythrough the inner column 2 to be sufficiently decomposed (depolymerized)in the primary and secondary decomposition temperature areas. Theexpanded plastic f is preferably heated for about 14-15 minutes beforeit is completely secondarily decomposed at about 600° C.

Different kinds of plastic raw material need to be treated at differenttemperatures. The storage section 1 is preferably held at temperatures(200-350° C.) at which the dissolved plastic mp can be expanded. Forgood decomposition, it is important to have a low temperature gradientto keep the expanded condition for a long time and to have a largecontact area with the heat. For this purpose, the decomposition column13 is preferably tilted relative to the horizontal. A hot air circulatesthrough the tilted decomposition column 13 from top to bottom with thehot air injected at the top. The temperature thus gradually increasesfrom bottom to top. This method is referred to as the so-called inversethermal gradient type.

To keep the good expanded plastic f for a long time, the decompositioncolumn 27 is preferably tilted at an angle θ of 25-30° as shown in FIG.2. For the decomposition column 27 tilted at an angle θ of less than25°, the expanded plastic may quickly flow transversely and disappear ina short time. For the column 27 tilted at an angle θ of higher than 30°,the gravity may make it hard to lift the expanded plastic f for a longdistance from the surface of the dissolved plastic mp, so that theexpanded plastic f may disappear again in a short time.

In FIG. 2, the storage section 29 for the dissolved plastic mp is formedat a connection that connects a supplying column 28 and thedecomposition column 27 in V shape. The supplying column 28 includes aninner column 20 and an outer column 21. A hot air is supplied betweenthose components via a pipe 22 to keep the temperature inside the innercolumn 20 at 200-350° C.

The decomposition column 27 includes an inner column 25, an outer column17, and a lead screw 24. The lead screw 24 is provided in thedecomposition column 27 such that the bottom of its shaft is rotatablysupported at the bottom wall of the storage section 29. A hot airproducer supplies a heated air of 450-620° C. into between the innercolumn 25 and the outer column 17 via a pipe 26 c. This heated air thencirculates through the decomposition column 27 by flowing down andexiting out of the pipe 26 b in the lower part of the decompositioncolumn 27 and flowing into the pipe 26 a in the upper part. The hot airthat thus circulates through the decomposition column 27 from top tobottom is able to increase the temperature in the decomposition column27 from bottom to top. The lower part of the decomposition column 27 isheld at 300-450° C. for the primary decomposition. The upper-part of thedecomposition column 27 is heated to about 600° C. for the secondarydecomposition.

The expanded plastic f occurs in the storage section 29. This expandedplastic f is then carried up in a good condition through the tilteddecomposition column 27 and heated on the way to provide the decomposedgas. The decomposition column 27 and a supplying section 28 areconnected in V shape and the dissolved plastic mp completely plugs thestorage section 29. The decomposed gas can thus safely prevent anybackflow from the decomposition column 27 to the supplying column 28. Itis also prevented that an external air flows through the storage section29 into the decomposition column 29, thereby eliminating any danger ofexplosion.

The plant for conversion into oil using the above described method forconverting plastic into oil will be described below.

In FIGS. 3-7, the plant for conversion into oil 30 according to thepresent invention includes, for example, a dissolution section 31, adecomposition section 32 for primarily and secondarily decomposing theplastic dissolved in the dissolution section 31, a dechlorinationtreatment section 33 for dechlorination in the treatment of thechlorine-including PVC, an off gas treatment section 34 for treating anoff gas generated in the dissolution and decomposition of the plastic,and the first and second hot air producers 35, 36 for generating a hotair which is a heat source for the dissolution and decomposition.

As shown in FIG. 6, the dissolution section 31 includes the firstdissolution column 31 a which connects via an unheated section 410 to ahopper 41 into which plastic raw material drops, the second dissolutioncolumn 31 b which has its back end connected under the front end of thefirst dissolution column 31 a and intersects the first dissolutioncolumn 31 a at right angles, the third dissolution column 31 c which hasits back end connected under the front end of the second dissolutioncolumn 31 b and intersects the second dissolution column 31 b at rightangles, and the fourth dissolution column 31 d which has its back endconnected under the front end of the third dissolution column 31 andintersects the third dissolution column 31 c at right angles. The firstto forth dissolution columns 31 a, 31 b, . . . , 31 d are thus arrangedtotally in a rectangle. The dissolved plastic is dropped and sent fromthe front end of the previous decomposition column to the back end ofthe next dissolution column serially. These dissolution columns 31 a-31d may also be connected horizontally.

As shown in FIG. 16, the hopper 41 includes a funnel-shaped casing 411,a cover 412 covering the top surface of the casing 411, a motor 413centered on-the cover 412, and a lead screw 414 including a rotatingshaft 414 a which connects to the motor 413 and extends through thecover 412 into the casing 411 and a spiral blade 414 b attached to therotating shaft 414 a. The spiral blade 414 b of the lead screw 414 istotally funnel shaped to the form of the casing 414. A distance W ofabout 2 to 5 cm intervenes between the inner wall of the casing 414 andthe periphery of the spiral blade 414 b. The motor 413 rotates the leadscrew 414 at a predetermined speed to prevent the light plastic fromblocking the hopper 41. The heavy plastic drops through the distance Wbetween the inner wall of the casing 414 and the periphery of the spiralblade 414 b. The lead screw 414 can reliably send the light plasticchips into the unheated section 410.

The unheated section 410 is column shaped and connected under the hopper41 (see FIG. 17). A motor 42 connects to the end of the unheated section410. This motor 42 connects to a lead screw 137 common to a lead screw137 in the dissolution column 31 a as described below. The motor 42rotates the lead screw 137 to slowly forward the plastic chips sent fromthe hopper 41 and supply them into the dissolution column 31 a. A hotair does not heat the unheated section 410, unlike the dissolutioncolumn 31 as described below. The attaching portion of the hopper 41 andthe dissolution column 31 are therefore separated. This can prevent theplastic from starting to dissolve near the attaching portion of thehopper 41 or the viscous resistance of the dissolved plastic fromstopping the rotation of the lead screw 137. Specifically, spacing thedissolved portion of the plastic apart from the attaching portion of thehopper 41 is able to provide a longer undissolved portion of the plasticthat presses forward the dissolved plastic.

The dissolution column 31 includes a rectangular outer case 136, and aninner column 131 in the outer case 136 (see FIG. 8). The inner column131 contains a lead screw including a rotating shaft 133 and a spiralblade 132 around the rotating shaft 133. The first dissolution column 31a includes a lead screw with a greater pitch than the lead screws 137 inthe other dissolution columns 31 b, 31 c, and 31 d. This is to provide alower retention density of the plastic to give a lower resistancebecause of the first dissolution column 31 a having a lower settemperature than the other dissolution columns as described below. Amotor rotates the lead screw 137. For example, a motor 42 rotates thefirst dissolution column 31 a (see FIGS. 4 and 5), and a motor 55rotates the second dissolution column 31 b.

A plurality of heatsink blades 134 reside around the inner. column 131.A hot air space 135 intervenes between the inner column 131 and theouter case 136. The first dissolution column 31 a is controlled to190-200° C., the second dissolution column 31 b is controlled to210-230° C., the third dissolution column 31 c is controlled to 230-260°C., and the fourth dissolution column 31 d is controlled to 300-340° C.These four dissolution columns 31 a, 31 b, . . . , 31 d are thusarranged in a rectangle with the temperature increasing with eachdissolution column. This is (a) to ensure a sufficient retention time(e.g., 20 minutes) to reliably dechlorinate the chlorine includingplastic such as polyvinyl chloride, (b) to provide a moderatetemperature distribution over multistage columns to help the temperaturecontrol, (c) to reduce the temperature in the first dissolution column31 a to prevent the adhesion of the plastic to the rotating shaft 133near the hopper 41, and (d) to provide a shorter installation length ofthe entire plant.

The first hot air producer 35 supplies a hot air via a pipe 70 to eachdissolution column 31. The producer 35 supplies the hot air fromdownstream to upstream of the column 31 in the carrying direction of theplastic. Each dissolution column 31 thus has an inverse thermalgradient. Blowers 56, 57, 58 (see FIG. 4), and 60 (see FIG. 7) circulatethe hot air through each dissolution column 31. A flue 59 connects tothe first and second hot air producers 35, 36. The flue 59 includesbranch pipes 59 a, 59 b, and an outlet 59 c, and is inverted U shaped(see FIG. 4).

The decomposition section 32 includes the first stage decompositioncolumn 47 controlled to 350-420° C. and the second stage decompositioncolumn 48 adjacent to the first stage decomposition column 47 andcontrolled to 450-580° C. (see FIG. 7). The decomposition columns 47, 48are tilted at 25-30° relative to the horizontal. The fourth dissolutioncolumn 31 d has an end that connects into the first stage decompositioncolumn 47. This connection forms the storage section for the dissolvedplastic.

The first stage decomposition column 47 includes two unit decompositioncolumns 47 a, 47 b, which are divided by a partition 256 into two rowsof left and right (see FIG. 9). The unit decomposition columns 47 a, 47b each include an inner column 255, a plurality of heatsink fins 253around the inner column 255, a lead screw 150, and a heat space 254 intowhich a hot air is sent. Each lead screw 150 includes a rotation shaft251 and a spiral blade 252. Motors 51 and 52 rotate the lead screws 150(see FIG. 5).

The second stage decomposition column 48 has almost the same structureas the first stage decomposition column 47. The second stagedecomposition column 48 has unit decomposition columns 48 a, 48 b (seeFIG. 6) which each have an inner column 148. The inner column 148contains a lead screw 149. Motors 53, 54 (see FIGS. 5 and 7) rotate thelead screws 149 slowly (4-5 revolutions per minute).

The inner column 255 in the first stage decomposition column 47 has atits upper end a superheat 151 for heating to 580-620° C. the decomposedgas flowing through the superheat 151 (see FIG. 7). The decomposed gasthat has been secondarily decomposed in the first stage decompositioncolumn 47 exits through the superheat 151 and pipe 49, and is sent tothe condenser 37 (see FIG. 5) via a scrubber 60 for alkali cleaning. Thecondenser 37 then cools the decomposed gas into oil, which is storedthrough a pipe 46 in an oil storage tank 42. Some of the oil stored inthe oil storage tank 42 is supplied to the hot air producers 35, 36 viaa service tank ST1.

On the way of the pipe 49 a valve 49 a resides for controlling the flowrate of the decomposed gas through the pipe 49. The condenser 37 needsto receive only the light decomposed gas that has been completelysecondarily decomposed in the first stage decomposition column 47. Thedecomposed gas derived from the pipe 49, however, may containincompletely secondarily decomposed gas that is slightly heavy. For asmaller amount of the decomposed gas derived from the pipe 49, theincompletely decomposed gas cannot go up the rising portion of the pipe49 and will be returned into the first stage decomposition column 47 andsent into the second stage decomposition column 48 via the fallingcolumn 120. For a larger amount of the decomposed gas derived from thepipe 49, the decomposed gas will be derived more strongly so that theincompletely decomposed gas can go up the rising portion of the pipe 49and will be sent to the condenser 37. The valve 49 a can thus adjust theamount of the decomposed gas derived from the pipe 49 to prevent theincompletely decomposed gas from being sent to the condenser 37.

The first stage decomposition column 47 is controlled to 350-420° C. asdescribed above. The first stage decomposition column 47 is thus able toprimarily and secondarily decompose the oil component corresponding togasoline with a low decomposition temperature, and some of the oilcomponent corresponding to coal oil and diesel oil. The superheat 151can completely secondarily decompose the insufficiently decomposedgases. The condenser 37 can cool into oil the decomposed gases that havebeen secondarily decomposed as described above. The pipe 46 with a pumpP can suck the gases that have been insufficiently converted into oil bythe condenser 37 and store them in the oil storage tank 42 as an offgas.

The expanded plastic component that has been incompletely secondarilydecomposed in the first stage decomposition column 47 is supplied to thebottom of the second stage decomposition column 48 via the fallingcolumn 120. The lead screw 149 in the second stage decomposition column48 will then send up the expanded plastic component at an angle. Thesecond stage decomposition column 48 is controlled to a temperature of450-580° C. The second decomposition column 48 can thus completelysecondarily decompose the residual portion of the componentcorresponding to coal oil and diesel oil, and the crude oil component.The residuals such as metal and dirt that have been dropped togetherwith the plastic will be stored in a sludge tank 40 via a sludge pipe 40a.

As shown in FIG. 18, the sludge tank 40 contains water 40 b. A metalgauge 40 c resides in the water 40 b, which collects the residuals.Taking the metal gauge 40 c out of the sludge tank 40 can remove theresiduals from the sludge tank 40. A cover 40 d with a partial opening40 e covers the top surface of the sludge tank 40. Inactive gas 40 fthat is heavier than the air, such as carbon dioxide gas, fills thespace above the water 40 b in the sludge tank 40. The sludge pipe 40 ahas its bottom in the inactive gas 40 f. A gas cylinder 40 g connects tothe sludge tank 40. The gas cylinder 40 g can supply into the sludgetank 40 the inactive gas 40 f, some of which overflows the opening 40 e.The inactive gas 40 f in which the sludge pipe 40 a has its bottom caneffectively prevent the air from flowing into the second stagedecomposition column 48 from the sludge pipe 40 a, thereby eliminatingany danger of explosion. The water 40 b in which the sludge pipe 40 ahas its bottom would float by the buoyancy the light residuals that mayblock the bottom of the sludge pipe 40 a. The inactive gas 40 f in whichthe sludge pipe 40 a has its bottom can prevent the above describedproblem and allow for the smooth falling of the residuals into the water40 b.

The second hot air producer 36 supplies a hot air via pipes 71, 71 a,and 71 b (see FIG. 5) to the upper parts of the first and second stagedecomposition columns 47, 48. The blowers 170, 171 can circulate the hotair through the decomposition columns 47, 48 by drawing the air out ofthe bottoms and returning it to the tops. The decomposition columns 47,48 thus have an inverse thermal gradient in which the temperaturedecreases from top to bottom. The first hot air producer 35 supplies tothe dissolution section 31 a hot air that is circulated, for example, bythe blower 60 through the fourth dissolution column 31 d (see FIG. 7).

The inner column 148 of the second stage decomposition column 48 has atits upper end a pipe 50 that connects to a condenser 38 via a scrubber61 for alkali cleaning (see FIG. 5). The decomposed gas that has beendecomposed in the second stage decomposition column 48 goes through thepipe 50 to the scrubber 61 and into the condenser 38. The condenser 38then cools the decomposed gas into oil, which goes through a pipe 86 toan oil storage tank 43. Some of this oil goes through a service tank ST2to the above described first and second hot air producers 35, 36. Acooling tower CT cools the above described condensers 37, 38 (see FIG.3).

The first and second stage decomposition columns 47, 48 include pipes101, 102 connected thereto, both of which connect to a collecting pipe100. The exhaust from the first and second stage decomposition columns47, 48 goes through the pipes 101, 102 to the collecting pipe 100 intothe outside. The pump P collects through the pipe 86 into the oilstorage tank 43 a gas that has not been converted into oil in thecondenser 38 which connects to the above described second stagedecomposition column 48.

Part of the foregoing dissolution column 31 and decomposition columns47, 48 uses an extendable column 700. The extendable column 700 includesa bellows portion 701 and a sliding portion 702 (see FIG. 19). Thebellows portion 701 includes a bellows 703 and a bellows inner column704 located in the bellows 703. The bellows inner column 704 has alonger full length than the bellows 703. The bellows 703 and bellowsinner column 704 are arranged with their ends aligned on one side. Thebellows inner column 704 extends beyond the other end of the bellows703. A support column 705 resides around the extended bellows innercolumn 704. These bellows inner column 704 and support column 705provide a sliding portion 702. The support column 705 has an innerdiameter that is slightly larger than the outer diameter of the bellowsinner column 704. The inner surface of the support column 705 and theouter surface of the bellows inner column 704 provide sliding surfaces.In FIG. 19, an inner column 706 with the same diameter as the bellowsinner column 704 resides on the portion of the support 705 on which thebellows inner 704 does not reside. Formed on the butt side ends betweenthe bellows inner column 704 and the inner column 706 are correspondingshoulders 704 a, 706 a. Opposite surfaces of the shoulders 704 a, 706 aprovide sliding surfaces.

The extendable column 700 provided in a part of the dissolution column31 and decomposition columns 47, 48 thus serves to absorb the expansionof the dissolution column 31 and decomposition columns 47, 48 that areheated and expanded. Specifically, for the first dissolution column 31 athat is heated from room temperature to about 200° C. and has a longerfull length due to expansion, the extendable column 700 provided in apart of the first dissolution column 31 a can reduce the bellows 703 toreduce the bellows inner column 704 toward the sliding portion 702 toabsorb the expansion of the first dissolution column 31 a.

In the extendable column 700 shown in FIG. 19, the sliding portion 702includes the bellows inner column 704 with its sliding area outside thebellows 701, and the support column 705 with the diameter larger thanthe bellows inner column 704. The bellows inner column 704 can thereforehave a greater thickness without reducing the inner diameter of thebellows inner column 704. This can prevent the deformation of theextendable column 700, therefore the damage of the bellows 703 due tothe deformed extendable column 700, and the fire due to the decomposedgases or the like flowing out of the damaged portion of the bellows 703.

The dechlorination treatment system 33 will now be described in detail.

Pipes 75, 76, and 77 extending from the upper surface of the dissolutioncolumns 31 a, 31 b, and 31 c of the dissolution section 31 connect to apipe 78 (see FIG. 5). The pipe 78 in turn connects to the firstseparator 37 (see FIG. 10). The first separator 37 can separate thehydrogen chloride gas generated in the dissolution sections 31 a, 31 b,and 31 c from the small amount of decomposed gas contained in thehydrogen chloride gas. The separator 37 includes a cooling coil 301 onthe top. The hydrogen chloride gas flowing through the pipe 78 will becooled through the cooling coil 301 and released in the lower part ofthe first separator 37 below the cooling coil 301. After being released,the hydrogen chloride gas goes through the cooling coil 301, the upperpart of the first separator 37, and a pipe 79 into the second separator38 that has the same structure as the first separator 37. After beingseparated in the second separator 38, the hydrogen chloride gas goesinto the third separator 39 that has the same structure as the first andsecond separators 37, 38. After being completely separated from thedecomposed gas in the third separator 39, the hydrogen chloride gas goesthrough a pipe 81 to the lower part of the reactor 300. A plurality ofthese separators 37, 38, and 39 can completely separate the hydrogenchloride gas from the decomposed gas.

The reactor 300 includes a stirring bar 306 with blades 308. A hydratedlime tank 83 connects to the upper part of the reactor 300. A heatingcolumn 305 resides around the hydrated lime tank 83 to dry the hydratedlime in the hydrated lime tank 83. A lead screw 303 resides at the lowerpart of the hydrated lime tank 83. A motor 304 rotates this lead screw303.

A lead screw 309 resides at the bottom of the reactor 303. A motor 310rotates this lead screw 309. A heating column 313 heats the surroundingarea of the lead screw 309 to dry and remove the water generated duringthe reaction in the reactor. A calcium chloride tank 312 contains thecalcium chloride generated during the reaction in the reactor 309.Temperature sensors S1, S2, and S3 reside at appropriate positions inthe height direction of the reactor 300. The temperature sensors S1, S2,and S3 detect the reaction heat. These reactor heat detection signalscan control the rotation of the motor 304 for the hydrated lime tank 83and the motor 310 for the lead screw 309 for evacuating the reactor 300.Specifically, the stirring bar 306 in the reactor 300 consistentlyrotates, and a large amount of hydrogen chloride gas flowing into thereactor 300 can facilitate the reaction to generate a large amount ofheat. The temperature sensor S3 at the highest position that detectsreaction heat equal to or greater than a predetermined value will causethe lead screw 303 for the hydrated lime tank 83 to rotate to send alarge amount of the hydrated lime into the reactor 300. Then thereaction proceeds to generate less reaction heat and slightly reduce thetemperature. When the temperature sensor S2 at an intermediate positiondetects a temperature in a predetermined range, the hydrated lime isaccordingly supplied. Then the reaction further proceeds to slow down.When the temperature sensor S1 at the lowest position detects apredetermined temperature, it determines that the reaction stops androtates the lead screw 309 for evacuating the reactor 300 and collectsthe calcium chloride generated into the calcium chloride tank 312. Afterthe calcium chloride generated being collected, when the reaction startsagain, the temperature sensor S1 detects the starting of the reactionand causes the lead screw 303 to rotate to send the hydrated lime fromthe hydrated lime tank 83 into the reactor 300. As the temperaturesensors S2, S3 detect the reaction heat in sequence, more hydrated limewill be supplied. As the reaction heat decreases, less hydrated limewill be supplied, and the above described procedure will be repeated.

It is said that the hydrogen chloride gas usually needs a solvent toreact with a dry neutralizing agent. Here, the water generated in thereaction of the hydrogen chloride gas with the hydrated lime can providethe solvent which can facilitate the neutralization reaction. Thereaction formula is as follows:2HCl+Ca(OH)₂=CaCl₂+2H₂O

A vacuum pump 314 resides to evacuate water that is generated as vaporin this reaction and draw the hydrogen chloride gas into the reactor300. To provide a constant suction load in the vacuum pump 314, a reliefvalve 315 for air inflow resides on the inlet side of the vacuum pump314. A scrubber 317 for alkali cleaning resides to remove the hydrogenchloride gas that has been insufficiently reacted in the reactor 300.

The off gas treatment system 34 will now be described.

FIG. 11 shows a schematic diagram of the off gas treatment system 34. Asshown in FIG. 11, the off gas treatment system 34 includes a casing 236.In the operation of the plant for conversion into oil, a burner 234 isconsistently connected to the casing 236, which is heated to about 1200°C.

The above-described casing 236 contains a plurality of ceramic prisms238, 238, . . . , 238. These ceramic prisms can catalytically crack anoff gas in {fraction (1/100)}-{fraction (2/100)} seconds that flows inthrough the inlet 235 connected to the above described oil storage tanks42, 43. The ceramic prisms can thus convert the off gas into a simpleoxide such as CO₂, NO_(x), and H₂O. The heat energy generated in thisprocess goes through the outlet 237 into the first and second hot airproducers 35, 36.

The off gas is an endocrine disrupter, such as acetaldehyde, which hasnot been converted into oil in the condensers 37, 38. In thisembodiment, after once collecting the off gas, the oil storage tanks 42,43 send it to the off gas treatment system 34. The condensers 37, 38 maydirectly send the off gas to the off gas treatment system 34.

The safety system in the tilted columns and the deodorant system willnow be described.

As shown in FIG. 20, a number of temperature sensors S, S, . . . Sreside on each dissolution column in the dissolution section 31 and eachtilted column in the decomposition section 32. Each sensor S connects toa controller 511. This controller 511 can control the open/close of avalve 513 connected to a carbon dioxide gas cylinder 512. This carbondioxide gas cylinder 512 connects to a hot air circulation path Pthrough which the first and second hot air producers 35, 36 can send thehot air into the dissolution section 31 and decomposition section 32.The controller 511 opens the valve 513 to supply the carbon dioxide gasthrough the hot air circulation path Q into the dissolution section 31and decomposition section 32, if the temperature sensor S detects anabnormal temperature due to such as accidents. This can cool thedissolution section 31 and decomposition section 32, and stop theoperation of the plant for conversion into oil 30.

An accumulation facility A for the plastic to be treated has at the topa suction unit 514 with a suction fan 514 a. The suction unit 514particularly sucks an air with an odor caused by the plastic waste andsends it to the hot air producer 36 for the deodorization by combustion.

Plastic chips P crushed by a crusher 515 are dried in a drier 516 withthe hot air from the hot air producer 36. The dried plastic chips P arethen sent to the hopper 41. The drier 516 in which the hot air dries theplastic chips P may be filled with an odor. The air with an odor in thedrier 516 is sent to the hot air producer 35 for treatment after acyclone 517 removes fine particles mixed in the air. These systems canprovide excellent deodorization.

The off gas treatment section 34 for the off gas treatment may decomposethe air with an odor. The hot air producer 35, 36 or the off gastreatment section 34, therefore, may treat the air with an odor.

The embodiments described above use two stages of the decompositioncolumns. The dissolution section 200 may be provided as follows: thesecond stage decomposition column 48 may precede the third stagedecomposition column 210 that has the same structure and the sametilting angle as the second stage decomposition column 48, as shown inFIG. 12. The temperature range may be of 350-400° C. in the first stagedecomposition column, 400-480° C. in the second stage decompositioncolumn, and 480-580° C. in the third stage decomposition column. Suchthree stages of the decomposition columns can provide a more moderatedistribution of the decomposition temperature and a longer decompositiontime, thereby making it possible to adapt to any change in thedecomposition condition such as the plastic specific gravity, and toensure the reliable secondary decomposition.

Specifically, the upper end of the second stage decomposition column 48connects, via a falling column 218, to the bottom of the third stagedecomposition column 210 tilted at the same angle. The second stagedecomposition column 48 sends the undecomposed expanded plastic anddecomposed gas that have not been extracted in the column 48 into thethird stage decomposition column 210 through the falling column 218. Thethird stage decomposition column 210 can secondarily decompose theundecomposed expanded plastic and decomposed gas. The secondarilydecomposed gas goes through a scrubber 216 for alkali cleaning into acondenser 213 which cools the decomposed gas into oil corresponding to Acrude oil. This oil goes through a pipe 214 into the oil storage tank215 where the oil is stored. A blower 221 connects to the third stagedecomposition column from the top to form an inverse thermal gradient.The residuals go through a sludge pipe 219 into a sludge tank 220 filledwith water where the residuals are stored. A pump P sucks the decomposedgas that has not been converted into oil in the above describedcondenser 213 of the third stage decomposition column 210. The pump Pthen sends the decomposed gas through the pipe 214 into the oil storagetank 215 where the gas is stored. The first and second stagedecomposition columns 47, 48 draw the secondarily decomposed gas out ofthe top for conversion into oil. A superheat 151, 152 decompose the gasthat has been insufficiently secondarily decomposed. The second stagedecomposition column can provide the decomposed gas that corresponds toa component of diesel oil, coal oil, and some of the crude oil. Thethird stage decomposition column can decompose the residual componentcorresponding to the A crude oil. More than three stages decompositioncolumns may be used.

The embodiment shown in FIG. 312 uses a dissolution section 200 that isformed vertically (perpendicularly). Specifically, the first, second,and third dissolution columns 201, 202, and 203 are connectedperpendicularly via connections 204, 205, respectively. The plastic fromthe hopper 41 goes right through the first dissolution column 201, leftthrough the second dissolution column 202, and right through the thirddissolution column 203 before being supplied to the bottom of the firststage decomposition column 47. A motor 208 rotates a lead screw 207 ofthe third dissolution column 203 at the lowest stage. The rotation ofthe motor 208 also rotates a lead screw 206 of the first dissolutioncolumn 201 via a chain 209. The rotation of the lead screw 206 in turnrotates a lead screw 212 of the second dissolution column 202 via gearsG1, G2 A blower 213 circulates a hot air up through the dissolutionsection 200 by drawing the air out of the top at a lower temperature tothe bottom at a higher temperature via a pipe 222.

In the embodiment shown in FIG. 21, a heating medium heating system 600supplies a heating medium which heats the first to fourth dissolutioncolumns 31 a, 31 b, . . . , 31 d. The heating medium here refers to aliquid heating medium such as various types of thermal oil. The heatingmedium heating system 600 heats the heating medium to a predeterminedtemperature and sends the medium through a heating medium pipe 601 intoa heating medium space 135′ of the dissolution column 31. The heatingmedium space 135 intervenes between an inner wall 131 and an outer case136, as for the above described hot air space 135. A circulation pump602 circulates the heating medium through the heating medium space 135from downstream to upstream. The first dissolution column 31 a iscontrolled to 190-200° C., the second dissolution column 31 b to210-230° C., the third dissolution column 31 c to 230-260° C., and thefourth dissolution column 31 d to 300-340° C., as in the above describedhot air heating.

The heating medium thus used instead of the hot air can a) greatlyimprove the heat transfer efficiency, b) reduce the temperature drop inthe dissolution column 31 when the plant stopped, because the heatingmedium cools less rapidly than the hot air, thereby allowing the plantto start up more quickly, and c) prevent the fire even if the innercolumn 131 of the dissolution column 31 is damaged.

The heating medium is used only for heating the dissolution column 31because the heating medium generally operates at 350 #1# or less. Anyother suitable heating medium, however, can be selected also to heat thedecomposition columns 47, 48. Depending on the temperature at which theheating medium operates, the heating medium may only heat thedissolution columns 31 that are controlled to lower temperatures (suchas first, second, and third dissolution columns 31 a, 31 b, and 31 c).

In the embodiment shown in FIG. 13, a connection 500 connects the fourthdissolution column 31 d and the lower part of the first stagedecomposition column 47. Through the connection 500, the column 31 dsupplies the dissolved expanded plastic into the bottom of the innercolumn 255 in the first stage decomposition column 47. The abovedescribed connection 500 may receive vegetable or animal cooking oil ortheir waste oil or the like stored in a tank 502. Each dissolutioncolumn primarily and secondarily decomposes the mixture of the oil andexpanded plastic. This can collect reformed oil through chemicaldecomposition reaction.

Generally, as shown in FIGS. 1-4, plastics such as polyethylene,polypropylene, polystyrene, ABS resin, and acrylic resin are thermallydecomposed into oil (90%) that is collected as the generated oil, an offgas (7-8%) that is treated in the off gas treatment system 34, andcarbide (2-3%) that is collected as the residual into the residual tank40. Polyvinyl chloride is neutralized by calcium hydroxide into calciumchloride (about 58%), and the residual (about 42%) is thermallydecomposed, but only about 30% is converted into oil and collected.

The disclosure of Japanese-patent application No. 2002-017650 (filed onJan. 25, 2002) including the specification, claims, drawings, andabstract, and Japanese patent application No. 2002-301895 (filed on Oct.16, 2002) including the specification, claims, drawings, and abstractare incorporated herein by reference in their entirety.

This invention is not limited to the embodiments described above. Theabove-described embodiments are illustrative, and any technical ideathat has the substantially identical configuration and operation as thetechnical idea set forth in the claims of the present invention isincluded in the technical scope of the present invention.

Industrial Applicability

As describe above, the method and plant for converting plastic into oilaccording to the present invention are useful as the method and plantfor converting plastic into oil for collecting the oil from the plasticwaste.

1. A method for converting plastic into oil, comprising: a dissolutionstep of heating and dissolving the plastic into expanded plastic; and adecomposition step of removing the expanded plastic, heating anddepolymerizing the expanded plastic, and cooling the expanded plasticinto oil.
 2. The method for converting plastic into oil according toclaim 1, wherein, in the decomposition step, the expanded plastic isremoved by being lifted at an angle.
 3. The method for convertingplastic into oil according to claim 1, wherein, in the decompositionstep, the expanded plastic is removed by being lifted at an angle of25-30° relative to the horizontal.
 4. The method for converting plasticinto oil according to claim 2, wherein, in the decomposition step, theexpanded plastic is heated with being lifted at an angle and theexpanded plastic is heated to higher temperatures at higher positions.5. The method for converting plastic into oil according to claim 1,wherein, in the dissolution step, the plastic is dissolved in adissolution section including a plurality of dissolution columns withdifferent temperature ranges.
 6. The method for converting plastic intooil according to claim 1, wherein, in the dissolution step, thedissolved plastic is added with vegetable oil or animal oil or mineraloil to generate expanded plastic of a mixture of the plastic and thevegetable oil or animal oil or mineral oil, and in the decompositionstep, the expanded plastic is removed, heated and depolymerized, andcooled into oil.
 7. The method for converting plastic into oil accordingto claim 1, wherein, in the decomposition step, the expanded plastic isremoved and heated in a decomposition section including a plurality ofdecomposition columns with different temperature ranges.
 8. The methodfor converting plastic into oil according to claim 1, further comprisinga hydrogen chloride gas treatment step of separating a hydrogen chloridegas generated in dissolving the plastic in the dissolution step fromother decomposed gases, then reacting the hydrogen chloride gas withhydrated lime, and collecting the hydrogen chloride gas as calciumchloride.
 9. The method for converting plastic into oil according toclaim 1, further comprising a off gas treatment step of treating an offgas not converted into oil in the decomposition step by catalyticallycracking the off gas with a hot ceramic.
 10. A plant for conversion intooil, comprising: a dissolution section for heating and dissolving theplastic into expanded plastic; and a decomposition section for removingthe expanded plastic, heating and depolymerizing the expanded plastic,and cooling the expanded plastic into oil.
 11. The plant for conversioninto oil according to claim 10, wherein the decomposition sectioncomprises removal means for removing the expanded plastic by lifting theexpanded plastic at an angle.
 12. The plant for conversion into oilaccording to claim 10, wherein the decomposition section comprisesremoval means for removing the expanded plastic by lifting the expandedplastic at an angle of 25-30° relative to the horizontal.
 13. The plantfor conversion into oil according to claim 11, wherein the decompositionsection comprises heating means for heating the expanded plastic withlifting the expanded plastic at an angle and for heating the expandedplastic to higher temperatures at higher positions.
 14. The plant forconversion into oil according to claim 10, wherein the dissolutionsection comprises a plurality of dissolution columns with differenttemperature ranges.
 15. The plant for conversion into oil according toclaim 10, comprising oil injection means for injecting vegetable oil oranimal oil or mineral oil into a connection between the dissolutionsection and the decomposition section.
 16. The plant for conversion intooil according to claim 10, wherein the decomposition section comprises aplurality of tilted decomposition columns with different temperatureranges.
 17. The plant for conversion into oil according to claim 10,further comprising a dechlorination system for treating a hydrogenchloride gas generated in the dissolution section, wherein thedechlorination system comprises a separator for separating the hydrogenchloride gas from other decomposed gases, and a reactor for reacting thehydrogen chloride gas separated by the separator with hydrated lime intocalcium chloride.
 18. The plant for conversion into oil according toclaim 10, further comprising an off gas treatment system for treating anoff gas not converted into oil after cooling in the decompositionsection by catalytically cracking the off gas with a hot ceramic. 19.The plant for conversion into oil according to claim 16, wherein each ofmultistage decomposition columns depolymerizes the plastic into adecomposed gas which is cooled into oil.
 20. The plant for conversioninto oil according to claim 16, wherein at least part of thedecomposition column comprises a superheat for further depolymerizingthe depolymerized plastic.
 21. The plant for conversion into oilaccording to claim 16, wherein the decomposition column is heated withincreasing temperatures from bottom to top.
 22. The plant for conversioninto oil according to claim 16, comprising residual collection means ata top of a final stage decomposition column of the multistagedecomposition columns.
 23. The plant for conversion into oil accordingto claim 22, wherein the residual collection means comprises a columnwith its upper opening at the top of the final stage decompositioncolumn and its lower opening in an atmosphere of an inactive gas heavierthan an air.
 24. The plant for conversion into oil according to claim10, further comprising a hopper for storing and supplying the plasticinto the dissolution section, wherein the hopper comprises a lead screwwith a spiral blade.
 25. The plant for conversion into oil according toclaim 24, further comprising an unheated section formed as an unheatedarea of a predetermined length between the hopper and the dissolutionsection.
 26. The plant for conversion into oil according to claim 14,wherein the plurality of dissolution columns each comprise a lead screwwith a spiral blade for carrying the plastic, a beginning dissolutioncolumn of the plurality of dissolution columns comprises the lead screwblade with a greater pitch than the lead screws blades in otherdissolution columns.
 27. The plant for conversion into oil according toclaim 14, wherein the dissolution section and the decomposition sectioneach comprise: an inner column; an outer column around the inner column;a hot air space between the inner column and the outer column andthrough which an hot air circulates; and a temperature sensor fordetecting a temperature in the dissolution section or the decompositionsection, and wherein the plant further comprises a carbon dioxide gassupplying system for supplying the carbon dioxide gas into the hot airspace if the temperature sensor detects an abnormal temperature equal toor greater than a predetermined temperature.
 28. The plant forconversion into oil according to claim 14, wherein the dissolutionsection and the decomposition section each comprise: an inner column; anouter column around the inner column; and a hot air space between theinner column and the outer column and through which an hot aircirculates, wherein the plant further comprises: a hot air productionsystem for generating by combustion the hot air to be supplied into thehot air space; and a drying system for drying the plastic to be suppliedinto the dissolution section, and wherein an air in the drying system issupplied into the hot air production system to be deodorized bycombustion.
 29. The plant for conversion into oil according to claim 18,further comprising a drying system for drying the plastic to be suppliedinto the dissolution section, wherein an air in the drying system issupplied into the off gas treatment system to be deodorized by beingcatalytically cracked with a hot ceramic.
 30. The plant for conversioninto oil according to claim 14, wherein an extendable column which isextendably formed is used in a part of the dissolution column includes,and wherein the extendable column comprises: an inner column; a bellowsaround the inner column which has one end fixed on the inner column andan other end slidable relative to the inner column; and an outer columnwhich is fixed on the other end of the bellows and slidably contains theinner column.
 31. The plant for conversion into oil according to claim10, wherein the dissolution section comprises: an inner column; an outercolumn around the inner column; and a heating medium space between theinner column and the outer column and through which a liquid heatingmedium circulates, and wherein the plant further comprises a heatingmedium supplying system for supplying the liquid heating medium into theheating medium space.